Embodiments of the invention relate to an apparatus and a method of compensating a seat offset for a load applied to the seat.
Automobiles are equipped with seat belts and airbags to restrain passengers. In recent years, there is a trend for controlling the operation of such safety devices according to the body weight of a passenger. For example, the amount of gas to be introduced into the airbag, an airbag inflating speed, or a pre-tensioning of the seat belt may be adjusted according to the weight of a passenger. Thus, to perform such adjustments the weight of the seat's occupant needs to be measured.
Several devices have been designed to measure the weight of an occupant while seated. Most of these devices use some form of sensor to measure forces transmitted to the seat. However, many of these devices do not provide an accurate measure of the occupant's weight because the sensor also measures additional forces other than the occupant's weight. Examples of these error-inducing loads include horizontal forces caused by assembly forces or an occupant in the rear of the vehicle pushing on the seatback, twisting moments caused by a leaning occupant, non-vertical load components caused by acceleration and deceleration of the vehicle, and the like. These error-inducing loads (or forces) can be transferred to the sensor and cause the sensor to generate incorrect information.
Thermal issues can also degrade the sensor. During seat installation, the seat is secured to the vehicle by forcing and twisting some metal parts of the seat into position. Once twisted and forced into position, the metal parts will generate forces generally referred to as preload. If the metal parts of the seat are heated by, for example, the sun, the heat accumulated in the seat and its metal parts relaxes the mechanical parts and changes the preload. In this way, the preload can also affect information from the sensor. Furthermore, information from the sensor can become inaccurate over time due to aging and wear of the sensor.